1. Field of the Invention
The present invention relates to an ink jet recording head for use in an ink jet recording system and a manufacturing method of the head.
2. Description of the Related Art
An ink jet recording head applied to an ink jet recording system includes a generally fine ink discharge port, a liquid flow path and an ink discharge energy generating element arranged in a part of the liquid flow path.
Heretofore, as a method of manufacturing such an ink jet recording head, U.S. Pat. No. 5,478,606 discusses a method having the following steps: (1) a step of forming a pattern which constitutes an ink flow path mold material of a soluble resin on a substrate on which ink discharge pressure generating elements are formed; (2) a step of dissolving a coating resin including a photosensitive resin, and coating a layer of the soluble resin with the solvent to thereby form a coating resin layer which constitutes an ink flow path wall on the soluble resin layer; (3) a step of forming the ink discharge ports in the coating resin layer above the ink discharge pressure generating elements; and (4) a step of eluting the soluble resin layer.
Usually in the above manufacturing method, the coating resin layer is formed of a photosensitive resin, the coating resin layer is exposed via a mask having an ink discharge port forming pattern, and then developed to thereby form the ink discharge ports. When the coating resin layer is formed of, for example, a negative photosensitive resin, this exposure is once performed on the whole surface of a region other than regions constituting the ink discharge ports. Moreover, at this time, exposure energy is set so that the coating resin layer develops sufficient adhesion to the substrate.
Moreover, as a liquid discharge head capable of coping with a high liquid droplet discharge speed, a liquid discharge head is also discussed in which a height of an ink flow path pattern (the mold material) manufactured in a manufacturing stage is changed so as to form the liquid flow paths having different heights (U.S. Pat. No. 7,036,909).
Here, in recent years, with development of a recording technology, highly precise recording has been demanded in an ink jet recording technology. As a method which meets such a demand, investigations of a method for minimizing ink droplets discharged from the ink jet recording head are advanced. The technique has a tendency to reduce a thickness (a thickness of an orifice plate) of the coating resin layer to be formed on the mold material and a tendency to reduce a diameter of each ink discharge port.
However, if the thickness of the orifice plate decreases, the coating resin layer above the ink flow path pattern might be excessively irradiated with the heretofore applied exposure energy, and sag and shape change of pattern edges might be generated. Therefore, it is difficult to highly precisely form micro ink discharge ports and polygonal ink discharge ports. Since light is transmitted through the coating resin layer, there is fear of an influence of reflection of the light from the substrate.
Furthermore, owing to the excessive irradiation, a part of the resin constituting the mold material is sometimes sensitized and depolymerized with the exposure energy transmitted through the coating resin layer. This depolymerized resin is easily damaged by a development liquid during the next developing step, and cracks might be generated. The generated cracks grow into voids in the mold material and an interface between the mold material and the coating resin layer owing to thermal history during the subsequent steps, finally destroy a protective material during anisotropic etching of the substrate and deteriorate a protecting function. This causes unstable ink discharge and deteriorates a printing quality owing to disturbance of an ink discharge direction. It is confirmed that as a diameter of each ink discharge port decreases, this phenomenon easily occurs.
Even in the liquid discharge head manufactured by changing the height of the mold material, there is a region where the orifice plate has a small thickness. Therefore, a problem similar to the above problem easily occurs.
If the exposure energy is reduced in order to inhibit the above sag and shape change of the pattern edges and inhibit the generation of the cracks in the mold material, it is difficult to secure sufficient adhesion between the coating resin layer and the substrate. That is, it has been difficult to manufacture an ink jet recording head capable of performing high-quality printing while securing the sufficient adhesion between the coating resin layer and the substrate, depending on the thicknesses of the orifice plate and the coating resin layer.